1. Field of the Invention
The present invention relates to a near-end of roll detecting apparatus that detects the amount that remains of a recording medium wound in a roll, and a printer that includes the near-end of roll detecting apparatus.
2. Description of the Related Art
Among printers that print on a recording medium that is, for example, wound in a roll is a printer that employs a so-called drop-in scheme of supporting from below, the recording medium wound in a roll and set dropped in the printer. In such a printer, the outer diameter of the recording medium wound in a roll varies with consumption of the recording medium. In such a printer, the position of the roll core portion in a center about which the recording medium is wound varies due to the weight of the recording medium and decreases in the outer diameter of the recording medium associated with consumption of the recording medium.
Conventionally, among drop-in-scheme printers is a printer that has a protrusion that engages with the roll core portion at the center of a recording medium, when the roll core portion has moved to a predetermined position, associated with consumption; and that is adapted to detect that the remaining amount of the recording medium is a predetermined amount or less, i.e., a so-called a near end by detecting the engagement of the protrusion with the roll core portion at the center of the recording medium wound in a roll.
For example, a conventional technology includes, for a paper feed roller, a unit that detects the number of rotations of a shaft and a unit that detects the number of rotations of a heat sensitive paper roll, and further detects the remaining amount of the heat sensitive paper roll by calculating the diameter of the heat sensitive paper roll from the difference between the number of rotations simultaneously detected (see, e.g., Japanese Patent Application Laid-Open Publication No. H5-16499).
As an example of a near-end of roll detecting technology, conventionally, for example, one technology includes a unit that detects a rotation time period that is necessary for a predetermined number of rotations or rotations corresponding to a predetermined angle of a roll when a rolled paper is fed being unrolled; a unit that detects the amount of the rolled paper fed when the predetermined number of rotations or the rotations corresponding to the predetermined angle of the roll is executed; and a computation processing unit that obtains paper remaining amount information by calculating the diameter of the roll at the time of the detection from the rotation time period and the amount of the rolled paper fed (see, for example, Japanese Utility Model Application Laid-Open Publication No. S62-136453).
Conventionally, for example, one approach involves calculating the rotation velocity of a roll paper fixing shaft that is a central shaft of the roll of paper being pulled out at a constant velocity, from a measurement of intervals of pulses generated using a slit plate and a sensor; comparing the temporal intervals of the pulses with a specific criterion; and, thereby, sensing the time when the roll of paper runs out (see, for example, Japanese Patent Application Laid-Open Publication No. H5-338335).
Another conventional paper remaining amount displaying scheme of displaying the remaining amount of a roll of paper that is conveyed being pressed by the roller, for example, includes a shaft rotation angle detecting unit that detects and outputs a rotation angle of a shaft of a roll of paper; a fed amount measuring unit that outputs, as the amount of paper conveyed, a rotation amount of a roller that presses and rotates the paper to be conveyed; and a remaining amount computing unit that computes and outputs the amount of paper that remains by receiving input of values output from the shaft rotation angle detecting unit and the fed amount measuring unit, respectively; where values output from the remaining amount computing unit are input to a remaining amount display unit for display (see, for example, Japanese Patent Application Laid-Open Publication No. H3-73746).
However, the conventional techniques, including the technique disclosed in Japanese Patent Application Laid-Open Publication No. H5-16499, are problematic in that although the amount that remains of a recording medium can be detected when the remaining amount becomes equal to or less than a predetermined amount, the specific amount that remains cannot be known. Therefore, for example, when a near end is reported during a busy period and printing is continued without replacement of the recording medium, an approximation of the actual amount that remains cannot be judged. Thus, a problem arises in that the recording medium runs out during the printing.
Each of the conventional technologies described in Japanese Utility Model Application Laid-Open Publication No. S62-136453, Japanese Patent Application Laid-Open Publication Nos. H5-338335 and H3-73746 is a technique of detecting the remaining amount of a recording medium when the recording medium rotates at a fixed position, that is, when the position of the center thereof is fixed. Therefore, a problem arises in that the remaining amount of the recording medium in a drop-in-scheme printer cannot be precisely reported.
To solve the problems associated with the above conventional technologies, an object of the present invention is to provide a near-end of roll detecting apparatus and a printer for a roll recording medium, that improve the precision in identifying the amount that remains of a recording medium.